The present invention relates generally to the aging of proteins resulting from their reaction with glucose and other reducing sugars, and more particularly, to the inhibition of the reaction of nonenzymatically glycosylated proteins and the often resultant formation of advanced glycosylation endproducts and cross-links.
The reaction between glucose and proteins has been known for some time. Its earliest manifestation was in the appearance of brown pigments during the cooking of food, which was identified by Maillard in 1912, who observed that glucose or other reducing sugars react with amino acids to form adducts that undergo a series of dehydrations and rearrangements to form stable brown pigments. Maillard, C.R. Acad. Sci., 154, pp. 66-68, (1912). Further studies have suggested that stored and heat treated foods undergo nonenzymatic browning as a result of the reaction between glucose and the polypeptide chain, and that the proteins are resultingly cross-linked and correspondingly exhibit decreased bioavailability.
This reaction between reducing sugars and food proteins was found to have its parallel in vivo. Thus, the nonenzymatic reaction between glucose and the free amino groups on proteins to form a stable, 1-deoxyketosyl adduct, known as the Amadori product, has been shown to occur with hemoglobin, wherein a rearrangement of the amino terminal of the beta-chain of hemoglobin by reaction with glucose, forms the adduct known as hemoglobin A.sub.1c. The reaction has also been found to occur with a variety of other body proteins, such as lens crystallins, collagen and nerve proteins. See, Bucala et al., "Advanced Glycosylation: Chemistry, Biology, and Implications for Diabetes and Aging," in Advances in Pharmacology, Vol. 23, pp. 1-34, Academic Press (1992).
Moreover, brown pigments with spectral and fluorescent properties similar to those of late-stage Maillard products have also been observed in vivo in association with several long-lived proteins, such as lens proteins and collagen from aged individuals. An age-related linear increase in pigment was observed in human dura collagen between the ages of 20 to 90 years. Interestingly, the aging of collagen can be mimicked in vitro by the cross-linking induced by glucose; and the capture of other proteins and the formation of adducts by collagen, also noted, is theorized to occur by a cross-linking reaction, and is believed to account for the observed accumulation of albumin and antibodies in kidney basement membrane.
In parent application Ser. No. 798,032, now U.S. Pat. No. 4,758,583, a method and associated agents were disclosed that served to inhibit the formation of advanced glycosylation endproducts by reacting with the early glycosylation product that results from the original reaction between the target protein and glucose. Accordingly, inhibition was postulated to take place as the reaction between the inhibitor and an early glycosylation product appeared to interrupt the subsequent reaction of the glycosylated protein with additional protein material to form the cross-linked late stage product. One of the agents identified as an inhibitor was aminoguanidine, and the results of further testing have borne out its efficacy in this regard.
While the success that has been achieved with aminoguanidine and similar compounds is promising, a need continues to exist to identify and develop additional inhibitors that broaden the availability and perhaps the scope of this potential activity and its diagnostic and therapeutic utility.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and compositions are disclosed for the inhibition of the advanced glycosylation of proteins (protein aging). In particular, the compositions comprise agents for inhibiting nonenzymatic cross-linking (protein aging) due to the formation of advanced glycosylation endproducts. The agents may be selected from those materials capable of reacting with the early glycosylation product from the reaction of glucose with proteins and preventing further reactions. Cross-linking caused by other reactive sugars present in vivo or in foodstuffs, including ribose, galactose and fructose would also be prevented by the methods and compositions of the present invention.
The agents comprise compounds having the following structural formula: ##STR1## wherein R.sub.1 is a hydroxy, lower alkoxy, amino or hydrazino group, or a group of the formula EQU --NR.sub.4 R.sub.5,
wherein R.sub.4 is hydrogen or lower alkyl, and R.sub.5 is an alkyl group of 1-20 carbon atoms, an aryl group, a hydroxy lower alkyl group, a cycloloweralkyl group or a heterocyclic group containing 4-7 ring members and 1-3 heteroatoms; or R.sub.4 and R.sub.5 together with the nitrogen form a morpholino, piperidinyl, or piperazinyl group; or when R.sub.4 is hydrogen, then R.sub.5 can also be a hydroxy group;
R.sub.2 is 0-3 amino or nitro groups, and/or a hydrazino group, a hydrazinosulfonyl group, a hydroxyethylamino or an amidino group; PA1 R.sub.3 is hydrogen or one or two fluoro, hydroxy, lower alkoxy, carboxy, loweralkylamino, dilower alkylamino or hydroxy loweralkylamino groups; PA1 with the proviso that when R.sub.1 is hydroxy or lower alkoxy, then R.sub.3 is a non-hydrogen substituent; PA1 with the further proviso that when R.sub.1 is hydrazino, then there must be at least two non-hydrogen substituents on the phenyl ring; PA1 and with the further proviso that when R.sub.3 is hydrogen, then R.sub.5 can also be an aminoimino, guanidyl, aminoguanidinyl or diaminoguanidyl group; PA1 their pharmaceutically acceptable acid addition salts and hydrates; and mixtures thereof, and PA1 a carrier therefor.
The compounds utilized in the compositions of this invention appear to react with an early glycosylation product thereby preventing the same from later forming the advanced glycosylation end products which lead to protein cross-links, and thereby, to protein aging.
The present invention also relates to a method for inhibiting protein aging by contacting the initially glycosylated protein at the stage of the early glycosylation product with a quantity of one or more of the agents of the present invention, or a composition containing the same. In the instance where the present method has industrial application, one or more of the agents may be applied to the proteins in question, either by introduction into a mixture of the same in the instance of a protein extract, or by application or introduction into foodstuffs containing the protein or proteins, all to prevent premature aging and spoilage of the particular foodstuffs.
The ability to inhibit the formation of advanced glycosylation endproducts carries with it significant implications in all applications where protein aging is a serious detriment. Thus, in the area of food technology, the retardation of food spoilage would confer an obvious economic and social benefit by making certain foods of marginal stability less perishable and therefore more available for consumers. Spoilage would be reduced as would the expense of inspection, removal, and replacement, and the extended availability of the foods could aid in stabilizing their price in the marketplace. Similarly, in other industrial applications where the perishability of proteins is a problem, the admixture of the agents of the present invention in compositions containing such proteins would facilitate the extended useful life of the same. Presently used food preservatives and discoloration preventatives such as sulfur dioxide, known to cause toxicity including allergy and asthma in animals, can be replaced with compounds such as those described herein.
The present method has particular therapeutic application as the Maillard process acutely affects several of the significant protein masses in the body, among them collagen, elastin, lens proteins, and the kidney glomerular basement membranes. These proteins deteriorate both with age (hence the application of the term "protein aging") and as a consequence of diabetes. Accordingly, the ability to either retard or substantially inhibit the formation of advanced glycosylation endproducts carries the promise of treatment for diabetes and, of course, improving the quality and, perhaps, duration of animal life.
The present agents are also useful in the area of personal appearance and hygiene, as they prevent the staining of teeth by cationic anti-microbial agents with anti-plaque properties, such as chlorhexidine.
Accordingly, it is a principal object of the present invention to provide a method for inhibiting the extensive cross-linking of proteins that occurs as an ultimate consequence of the reaction of the proteins with glucose and other reactive sugars, by correspondingly inhibiting the formation of advanced glycosylation endproducts.
It is a further object of the present invention to provide a method as aforesaid which is characterized by a reaction with an initially glycosylated protein identified as an early glycosylation product.
It is a further object of the present invention to provide a method as aforesaid which prevents the rearrangement and cross-linking of the said early glycosylation products to form the said advanced glycosylation endproducts.
It is a yet further object of the present invention to provide agents capable of participating in the reaction with the said early glycosylation products in the method as aforesaid.
It is a still further object of the present invention to provide therapeutic methods of treating the adverse consequences of protein aging by resort to the aforesaid method and agents.
It is a still further object of the present invention to provide a method of inhibiting the discoloration of teeth by resort to the aforesaid method and agents.
It is a still further object of the present invention to provide compositions including pharmaceutical compositions, all incorporating the agents of the present invention.
It is a still further object of the present invention to provide novel compounds useful in the methods of this invention, as well as processes for their preparation.